Suggestions regarding visit to mountreux Switzerland/ Naples-Capri Italy

How long do you have?
What month?
Interests?
How many in traveling party/ages?

Yes, the amount of time you can spend is an important factor. Seems like an odd choice since they are so far apart.

I have only 1 day,we are 4 adults and 2 small children 3 and 6years of age probably wish to visit after 1 month.as we heard,both sites are enriched with beauty of nature, but due to tight schedule, we can go either mountreux or Naples-Capri

Where else are you going on this trip? These two destinations are so far apart that neither of them make sense for just 1 day unless you are staying the somewhere reasonably close the night before. To sightsee both Naples and Capri you also really need a day for each.

And where are you going AFTER this 1 day (+ 1 night?) stay?

We have 2 days for paris,, 1 day,for either mountreux Switzerland or Naples-Capri, and 2days for Rome ,1day for pisa ,and lastly 2 days for Venezia

You'll be getting an overwhelming amount of advice to add the extra day to one of your existing cities instead of a new location. 2 days in Paris or Rome barely scratches the surface. I would also argue that dedicating an entire day to Pisa isn't a great use of time. How are you moving between locations? Does the number of days include travel days or is the the full number of days on the ground?

That's a REALLY tight schedule, especially with two young children, and especially in August heat, if that's the month you intend to travel. You'd spend more time getting from place to place than seeing much at all.

To be honest, with just 8 days to work with I'd drop Switzerland, Capri/Naples and Pisa altogether and do 3 days/4 nights in Paris, 3 days/4 nights Rome, and 2 days/3 nights in Venice.

You could also do 3 days/4 nights in Paris; 2 days/3 nights in Naples; day trip by ferry to Capri from there; 3 days/4 nights Rome but even that feels a little rushed to me.

Thanks for kind suggestions, we will try reschedule,our tour keeping your suggestions in mind.In our existing program,journey days are excluded

If that is the case I would suggest Paris, Venice, Rome/Naples. Keep in mind Paris-Venice is a long travel day. Over 10 hours by train.
Venice to Rome is 3.5 hours. Best of luck on your travels and enjoy.

They could also fly from Paris to Venice, train to Rome, flight from Rome home or to ???

At Rome our tour will finish,will back to pakistan,my home country.I am extremely thankful,for your time you spared writing the wonderful suggestions...thanks again

Just to add, if you decide to do the Paris> Naples> Rome option, fly to Naples. You can do Naples> Rome via fast train: only takes 70 minutes or so.

This is another good suggestion, I have a little bit different option,that I'm thinking of, from paris>vce(by air) then vce to naple by air,then naple to Rome by train